1. Field of the Invention
This invention relates generally to medical methods and systems and more specifically to methods for assessing the functionality of lung compartments.
2. Description of the Related Art
Lung diseases are a problem affecting hundreds of millions of people worldwide. Chronic obstructive pulmonary disease (COPD), for example, is a significant medical problem affecting about 16 million people in the U.S. (or about 6% of the U.S. population) and many millions of people around the world. Lung cancer, as another example, is among the most prevalent forms of cancer, and causes more than 150,000 deaths per year. In general, two types of diagnostic tests are performed on a patient to determine the extent and severity of lung disease: 1) imaging tests, and 2) functional tests. Imaging tests, such as chest x-rays, computed tomography (CT) scans, Magentic Resonance Imaging (MRI), perfusion scans, and bronchograms, provide a good indicator of the location, homogeneity and progression of the diseased tissue. However, these tests do not give a direct indication of how the disease is affecting the patient's overall lung function and respiration capabilities. This can be measured with functional testing, such as spirometry, plethysmography, oxygen saturation, and oxygen consumption stress testing, among others. Together, these diagnostic tests are used to determine the course of treatment for the patient.
Currently available diagnostic tests for COPD, however, are limited in the amount and type of information that may be generated. For example, diagnostic imaging may provide information to the physician regarding which lung regions “appear” more diseased, but in fact a region that appears more diseased may actually function better than one that appears less diseased. Similarly, functional testing is performed on the lungs as a whole. Thus, the information provided to the physician is generalized to the whole lung and does not provide information about functionality of individual lung compartments, which may be diseased. Thus, physicians may find it difficult to target interventional treatments to the compartments most in need and to avoid unnecessarily treating compartments that are least in need of treatment. Therefore, in general, using conventional imaging or functional testing involving the whole lung, the diseased compartments cannot be differentiated, prioritized for treatment, or assessed after treatment for their level of response to therapy. Consequently, there is a need for better indicators of localized disease progression as well as methods for measurement of these indicators.
One useful indicator of disease progression is the elasticity of the airways of the given lung compartment. In a lung affected by a COPD such as emphysema, there is permanent enlargement of the alveoli due to the destruction of the walls between alveoli. The destruction of the alveolar walls reduces the elasticity of the corresponding lung compartment during the respiratory cycle. Loss of elasticity leads to collapse of the bronchioles, obstructing airflow out of the alveoli. Air becomes “trapped” in the alveoli, which reduces the ability of the lung to contract during exhalation. The reduced expansion of the lung during the next breath reduces the amount of oxygenated air available for gaseous exchange. Further, the trapped air also can compress adjacent, less damaged lung tissue, preventing it from functioning to its fullest capacity. It would therefore be advantageous to identify those portions of the lung that are most severely affected by COPD and treat those areas by localized lung volume reduction methods.
Localized diagnostic methods for identifying and quantifying diseased lung portions have been disclosed in the following co-pending U.S. Patent applications assigned to the assignee of the present application: U.S. Pub. Nos. 2007/0142742 and 2008/0200797, the full disclosures of which are hereby incorporated by reference. The '742 application discloses ways of locally measuring collateral ventilation, while the '797 application discloses several concepts for localized lung diagnostics including collateral ventilation and lung compliance measurement, and devices and systems for such measurement.
The detection of loss of elasticity of lung tissues is a method that would be desirable for tracking the progression of COPD in affected patients. In a normally functioning lung or compartment, the elasticity of the tissues enables expulsion of inhaled air, while in an affected lung or lung portion the loss of elasticity manifests as an inability to expel air. This is apparent in the various characteristics of inspiratory or expiratory air flow. For example, the pressure exerted during exhalation is a measure of lung elasticity, and local (lobar) measurement of exhalation pressure can provide an indicator of disease progression. Although pressure measurement has been used in relation to several types of respiratory conditions, there is no known use of exhalation pressure for diagnostic purposes.
Pressure measurements outside the body have been disclosed in other conditions, for example, in relation to sleep apnea. Such measurement of pressure during respiration is disclosed in several references such as U.S. Pat. No. 4,667,669 to Pasternack, U.S. Pat. No. 5,161,525 to Kimm et al. and U.S. Pat. No. 5,720,709 to Schnall. However, the apparatus disclosed in these applications measure pressure variations detected at the mouth or external to the lung. The pressure variations are therefore indicative of the properties of the entire lung and do not provide data from the diseased portions alone. U.S. Pat. No. 6,066,101 to Johnson et al. and U.S. Pat. No. 7,094,206 to Hoffman disclose methods of measuring respiratory resistance of the lungs. The system includes a pneumotach, into which the patient breathes normally. In both the references, the measurement method uses pressure transducers to measure pressure variations during inhalation and exhalation. The references further include methods for analysis of the data to obtain data on lung function and alveolar function. However, as with devices intended for sleep apnea, these methods are external and do not provide diagnostic information pertaining to localized diseased lung portions. Rather, they provide an average value for the entire lung. This is disadvantageous, as certain compartments maybe more affected by disease than others, yet since the diagnosis is of the entire lung, only the entire lung may be treated.
Pressure measurements within the lung have also been used in the diagnosis of asthma and emphysema, as disclosed in U.S. Pat. No. 6,634,363 to Danek et al. and U.S. Pat. No. 6,692,494 to Cooper et al. and U.S. Patent Application number 2006/0254600 to Danek et al. The '363 patent and the related '600 application concern asthma treatment and disclose diagnosing lung sensitivity to asthmatic stimuli by stimulation of a portion of the lung, followed by pressure measurement to detect constriction and reversible constriction of the airways. However, it does not reveal information on the elasticity of lung tissue that would aid in diagnosis of COPD. Similarly, the '494 patent discloses measurement of change in pressure within an occluded lung compartment. This measurement is made, however, for quantifying collateral ventilation, and does not provide information on lung tissue elasticity.
Therefore, it would be advantageous to have methods and systems for more accurately diagnosing and/or pinpointing COPD in the lungs. Ideally, such methods and systems would provide information regarding elasticity of the lungs, and more specifically information regarding elasticity of various portions of the same lung. In doing so, such lung assessment methods and systems would help a physician more accurately and effectively assess lung function and disease and thus develop more effective treatment strategies.